An image processing apparatus such as a laser printer is provided with a photosensitive drum having electrostatic latent images formed thereon, a process cartridge having a developing roller for supplying developer to the photosensitive drum and a developer cartridge having developer accommodated therein. For example, JP-A-9-319202 discloses an image forming apparatus including a supply opening for supplying developer in a developer cartridge to a developing chamber, a developer cartridge having formed therein a return opening for returning developer from the developing chamber to the inside of the developer cartridge, an agitator having blades for agitating the interior of the developer cartridge and an auger capable of conveying developer within the developing chamber at a supply opening side toward a return opening side. In the related developer cartridge, the developer agitated by the rotation of the agitator is circulated in such a manner that after it is discharged through the supply opening to the developing chamber, it is conveyed toward the return opening side by the auger and then returned through the return opening to the inside of the developer cartridge. Therefore, fresh developer can be supplied from the cartridge.